Reduction of aromatic nitro compounds.



No. 736,206. 'PATBNTED AUG. 11.1903. M. BUGHNER.

REDUCTION OF AYROMATIG NIIRO COMPOUNDS.

APPLICATION. IILBD DEC. 14. 1901.

Q N0 MODEL.

Q'vi (Human Patented August 11, 1903.

UNITED STATES PATENT OFFICE.

MAX BUCHNER, OF MANNHEIM, GERMANY, ASSIGNOR TO 0. F. BOEHRINGER dz SOEHNE, OF MANNHEIM-WALDHOF, BADEN, GERMANY, A FIRM.

REDUCTION OF AROMATIC NITRO COMPOUNDS.

SPECIFICATION formingpart of Letters Patent No. 736,206, dated August 1 1, 1903..

- Application filed December 14, 1901. Serial No. 85,956. l (N specimens.)

To all whom it may concern.-

Be it known that 1, MAX BUCHNER, a citizen of the German Empire, residing at Mannheim,

i and useful Improvement in the Reduction of Aromatic Nitro Compounds and I do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same.

This invention relates to the art of reduc ing nitro compounds, its object being the reduction of such bodies to the corresponding amins. In this art it has hitherto been possible as a general thing to elfect such reduction only when the nitro body to be reduced was suspended in an acid-bath. Only in some special instances where such reduction phase was aided by apparently constitutional conditions had it been possible to reduce a nitro body electrolytically to the corresponding amin in an alcoholic alkaline solution. (Elbs, Zeitschmftfitr Elcctro- U7zemie,V, p. 113, and Rhode, ibid, VII, pp. 328, 338.)

i No general practically available process is, however, known at the present time whereby any nitro compound can be converted in sufficient quantity into the corresponding amin from anaqueous alkaline bath, which may be a solution or a suspension and irrespective of the constitution of the starting material to.

be reduced. I have found in my researches in this field that nitro bodies dissolved or sus pended in alkaline baths or baths containing a salt, oxid, or other compound of an alkali may be reduced to the corresponding amins if a cathode, preferably one of copper, is employed, together with powdered copper. The process conducted on these lines, I find, will effect the desired reduction with all nitro bodies thus far examined. As an example I may state that with the aid of the same I have been enabled to readily reduce meta-nitraniline to meta-phenylene-diamin, although Elbs and Kopp were not able' to obtain any diamin from the same, according to their method. (Zet'tschrz'ft fitr Electro- Chemt'e,V, p. 108.)

Under my process the current energy is as a general thing almost entirely utilized in the work of reduction, the yield in the corresponding amin being slightly less than quantitative. Only where the amin formed is chemically changed by the alkali is there any considerable loss of energy. The bases formed, particularly those existing in a liquid form, are isolated by very simple methods, which are so well known as to need no detailed description. The reaction takes place in the same manner if the solution or mixture of the nitro compoundin the cathode-bath is facilitated by the addition of an indifferent organic solvent,such as alcohol. Moreover, the oxids or salts of the alkalies may be replaced by the corresponding compounds of the earthy alkalies, and these are therefore the equivalents of the former.

The electrolytic reduction of the nitro bodies above set forth out of baths containing salts or compounds of alkalies or earthy alkalies may be combined with the production of alkalies or earthy alkalies and chlorin, which involves a very considerable advantage over the reducing methods from acid solutions or baths as hitherto practiced. I have further found that the employment of a copper cathode, though preferable, is not indispensable in carrying out my process, but that instead cathodes of other cathode materials may be I employed if copper or one of its salts or compounds be added to the electrolyte. All cathode materials which I have thus far investi gated in connection with this process have answered and led to the reduction of the nitro bodies. invention, broadly considered, involves the It is therefore to be noted that my use of an alkaline bath for reducing nitro compounds to the corresponding amin in combination with copper or a salt or compound of copper added to the electrolyte.

By the term alkaline bath when employed in the claims I desire to cover either a bath of alkali or earthy alkali proper or a bath containing asalt or other compound of an alkali or earthy alkali or a mixture of such baths. My invention,moreover,involves such other steps, features, and methods as will he hereinafter set forth and pointed out in the claims.

In order to enable others to fully understand my invention, I Will now give a detailed description of the same with the aid of a number of examples embodying what I consider the preferred method of carrying the same into effect.

I. Reduction of Nttrobenzene (C II .NO t0 And in (O l'l Nll geously employed, and use in connection with is from 80 to 86 c'entigrade.

the same an anode of carbon or other indifferent material. The cathodechamber is provided with a good stirring device and a coiled pipe, which may serve both for cooling or heating the cathode-bath, according to need. Into the cathode-chamber thus equipped I introduce the cathode-bath, as follows: I pour one thousand four hundred and forty parts, by weight, of a concentrated solution of sodium chlorid, fifty to one hundred parts, by weight, of powdered copper, and one hundred and twenty-three parts, by weight, of nitrobenzene. The latter is preferably added gradually. The cathode employed in this example is one of copper. NVhen all the materials are added, the reduction is preferably carried out with a current density of about fifteen hundred amperes per square meter and a temperature of about 80 to 100 centigrade. The cathode-bath is stirred, so as to keep the ingredients well mixed. will under those conditions amount to about five volts.' The process is discontinued after the amount of current calculated for the complete reduction to anilin has passed through the cell. The greater portion of the anilin thus obtained may be directly drawn off, while the rest may be isolated by well-known methods.

(1)) Employment of a copper cathode in alcoholic solution.The cathode-chamber of the apparatus described. under Example I" is charged with one thousand parts, by weight,-

of a four-per-cent. solution of caustic soda (NaHO), two hundred and fifty parts, by weight, of alcohol, and one hundred parts, by weight, of copper powder, and the anodespace with a twelve-per-cent. solution of cans tic soda. To the cathode-bath so prepared there are added gradually one hundred and twenty-three parts, by weight,'of nitrobenzene. The currentdensity employed for the electrolysis is fifteen hundred amperes per square meter, and the temperature of the bath A copper cathode is employed.

(0) Employment ofa harinm-chlorid hath.- The cathode-chamber is charged with one hundred and twenty-three parts, by weight, of nitrobenzene, one thousand parts, by weight, of a-thirty-per-cent. aqueous solution of barium chlorid, and one hundred parts, by weight, of powdered copper,and the anode-space with a thirty-per-cent. solution of barium chlorid. The current density employed is fifteen hun- The tension of the bath dred amperes to the square meter. The other conditions of the process are the same as in Example I. w

(d) Employment of a platinum cathode in presence of powdered copper.-The electrolytic cell is again subdivided into an anode and a cathode space by means of a diaphragm. Into the former, which is provided with a carbon or other indifferent electrode, a saturated solution of common salt (NaCl) is introduced. Into the cathode-space, which is equipped with a platinum electrode, an effective stirring device, and a platinum coiled pipe for cooling or heating the bath, there are introduced one thousand four hundred and forty parts, by weight, of saturated salt solution (NaOl), and about one hundred parts, by weight, of finely-divided copper powder. A current of a density of fifteen hundred to two thousand amperes per square meter of cathode-surface is now passed through the cell, and one hundred and twenty-three parts, by weight, of nitrobenzene are gradually introduced into the red notion-chamber. The electrolysis is preferably carried out at a temperature of from to 100 centigrade, and the current is cut off after the quantity of current calculated to be required for the complete reduction has passed through the cell. The anilin thus obtained is then isolated and purified according to known methods. The yield is very good.

(e) Employment of a tin cathode tn presence of divided copper.The apparatus and conditions of process and proportions are the same as under the foregoing example, with the exception that instead of a platinum cathode one of tin is employed. The yield of anilin is .very good.

(f) Employment of a copper cathode tn the presence of cuproas chlortd..-The apparatus and conditions of process are the same as under Examplel, with the exception that instead of the copper powder about one hundred parts, by weight, of cuprous chlorid are added to the cathode-bath.

(g) Employment of a nickel cathode tn the presence of copper sulfate-The cathode-space is charged with one thousand four hundred and forty parts, by weight, of concentrated solution of common salt (NaOl) and one hundred parts, by weight, of sulfate of copper (blue vitriol) and equipped with a nickel cat11- ode. In other respects the conditions of the process are the same as under Example I.

II. Reduction of Orthonttrotoluene (O ILCH N0 to Orthotolnidtn (O II CIL NH The apparatus for carrying out the process for this reduction is arranged as in the first example or Example I. Into the cathode- IIO toluene, are introduced. In other respects the process is the same asunder Example I The resultant o-toluidin is isolated by known methods; 1

III. Reduction of Meta Nitrdnilin e u,- NOQNHQ) to llletct Phenylcne Dz'cmm'n (can. 2NH2).

C The apparatus employed and steps and conditions of the process under this example are thesame as under the first example-viz. I with the exception that the cathode-bath is to consist of one thousand four hundred and forty parts, by Weight, of a concentrated solutionof ordinary salt, fifty to one'hundred parts, by weight, of comminuted copper, and

i one hundred and thirty-eight parts, by weight,

of meta-nitranilin. The resulting meta-phenlution or suspension according to well-known methods.

The yield is about eighty per cent. As seen from this example, a very good yield of the amin is obtained according to my method, which is contrary to theoretical views and the experiments made by Ebbs and Rhode,

(Zeitschwftfflr Electro-Ohemie, XXII, p. 340,

1890,) which resulted in the formation of the azo compound. I

IV. Reduction of Alpha Nitronaphthalt'n .(O ILNOQ t Alpha Naphth'ylamin Here again I proceed as under Example I,

introducing into the cathode-compartment a mixture of one thousand four hundred and forty parts, by weight, of concentrated salt (sodium chlorid) solution, from fifty to one hundred parts, by weight, of powdered copper, and one hundred and seventy-three parts,

.by weight, of alpha-nitronaphthalin. The rer'sultant alpha-naphthylamin is isolated according to known methods. It will be understood, of course, that in the above examples one cell or any desirable or suitable number of cells in a battery may be employed at one time and that any convenient and suitable electrolizing apparatus may be used, it being manifest that the process claimed by me is not confined to any particular form of apparatus. 6

metals. The fact that the electrolyte-bath may contain either a compound of an alkali metal or of an alkaline-earth metal for the purposes of this invention is to be borne in mind in construing the claims formingpart of this specification. It is to be noted also that the process embodying my invention is carried out in some instances when the ingredients of the cathode-bath are in solution and in others when they are partly suspended in the bath. These different conditions of the bath I express generically in the claims by stating that the substance to be reduced is mixed with the electrolyte.

In the accompanying drawing I have represented one out of the many possible forms of apparatus and electrolytic cells for carrying out the process involved in. my invention.

In the drawing, A represents the anodechamloer, containing the anode electrolyte, and a the anode; O, the cathode-chamber, containing the cathode electrolyte, and c the cathode, while (1 represents a diaphragm of any suitable material for the separation of the two electrolytes, according to the usual manner.

S represents a suitable stirrer arranged within thecathode electrolyte, the spindle or shaft s-of which may be connected with any suitable source of power bya belt and pulley B P, as shown, or in any preferred way. The cooling of the cathode-compartment may be effected by a cooling-coil T, arranged within the said cathode -compartment, as shown, said coil serving for the circulation of any cooling fluid, such as cold water.

1. The process of reduction which consists in passing an electric current through the substance to be reduced in an electrolyte containing a compound of an alkali metal or of an alkaline-earth metal,in thepresence of copper.

2. The process of reduction which consists in passing an electric current through a nitro compound contained in an electrolyte .containing a compound of an alkali metal or of an alkaline-earth metal, in the. presence of copper.

3. The process of reduction which consists in passing an electric current through the substance to be reduced in an alkaline electrolyte in the presence of copper. r

4. The process of reduction which consists in passing an electric current through a nitro compound in an alkaline electrolyte in the presence of copper.

5. The process of reduction which consists in passing an electric current througha nitro compound of the aromatic series containedin an electrolyte containing a compound of an alkali metal or of an alkaline-earth metal, in the presence of copper, until the correspond ing amin is produced.

6. The process of reduction which consists in mixing the substance to be reduced with an alkaline electrolyte containing copper, and passing the electric current through the same.

7. The process of reduction which consists in mixing a nitro compoundwith an electrolyte containing a compound of an alkali metal or of an alkaline-earth metal, and copper, and

passing the electric current therethrough.

. earth metal, and copper, andpassing the electric current therethrough.

9. The process of reduction which consists in mixing a nitro compound of the aromatic series with an alkaline electrolyte containing copper, and passing the electric current therethrough.

10. The process of reduction which consists in mixing a nitro compound with cathodebath, containing a compound of an alkali metal or of an alkaline-earth metal, and passing an electric current therethrough in the presence of a copper cathode.

11. The process of reduction which consists in mixing a nitro compound with an alkaline cathode-bath and passing an electric current therethrough in the presence of a copper cathode.

12. The process of reduction which consists in mixing the compound to be reduced with an electrolyte containing a compound of an alkali metal or of an alkaline-earth metal, and copper and passing an electric current therethrough. 13. The process of reduction which consists in mixing the compound to be reduced with an alkaline electrolyte containing copper, and passing an electric current therethrough.

14. The process of reduction which consists in mixing the compound to be reduced with an electrolyte containing a compound of an alkali metal or of an alkaline-earth metal, and finely-divided metallic copper, and passing an electric current therethrough.

15. The process of reduction which consists in mixing the compound to be reduced with a cathode-bath containing a compound of an alkali metal or of an alkaline-earth metal and copper, and passing the electric current therethrough inthe presence of a coppercathode.

16. The process of reduction which consists in mixing the compound to be reduced with a cathode-bath containing a compound of an alkali metal or ofanalkaline-earth metal, and

finely-divided'metallic copper, and passing an electric current therethrough in the pres ence of a copper cathode.

17. v The process of reduction which consists in mixing a nitro compound with an electrolyte containing an alkali compound and copper, and passing an electric current therethrough.

18. The process of reduction which consists in mixing a nitro compound with an electrolyte containing a compound of an alkali metal or of an alkaline-earth metal, and finely-divided metallic copper, and passing an electric current therethrough.

19. The process of reduction Which consists in mixing a nitro compound with a cathode, bath containing a compound of an alkali metal or of an alkaline-earth metal, and copper, and passing the electric current therethrough in the presence of a copper cathode.

20. The process of reduction which consists in mixing a nitro compound with a cathodebath containing a compound of an alkali metal or of an alkaline-earth metal, and finely-divided metallic copper, and passing an electric current therethrough in the presence of a copper cathode.

21. The process of reduction which consists in mixinga nitro compound'of the aromatic series with an electrolyte containing a compound of an alkali metal or of an alkaline earth metal, and finely-divided metallic copper, and passing an electric current therethrough.

22. The process of reduction which consists in mixing a nitro compound of the aromatic series with a cathode-bath containing a compound of an alkali metal or of an alkalineearth metal, and copper, and passing the electric current therethrough in the presence of a copper cathode.

23. The process of reduction which consists in mixing a nitro compound of the aromatic series with a cathode-bath containing a compound of an alkali metal or of an alkalineearth metal, and finely-divided metallic cop per, and passing an electric current therethrough in the presence of a copper cathode. In testimony whereof I afiix my signature in presence of two witnesses.

V, ,5 MAX BUOI'INER.

Vitnesse's:

EDWARD KoBNER, J AOOB ADRIAN. 

